Hello all~ I'm new to K2 and learning about FirExp...

# compiler

[Ng Hui Qin]

Hello all~ I'm new to K2 and learning about FirExpression. If I want to build simple function as below in FIR

fun simpleFunction(): Int = TODO()

How could I build expression to present : Int = TODO() in FirFunction?

Try using example in https://github.com/JetBrains/kotlin/blob/master/docs/fir/fir-basics.md, I guess the direction is like

val myFunction = buildSimpleFunction {
    name = Name.identifier("simpleFunction")
    ... << starting here I lose my direction in building return type, equal token and TODO() expression
}

[Ng Hui Qin]

If anyone could share me the pointer of simple examples FirExpression build will be great!

[dmitriy.novozhilov]

In the original design it's expected that on frontend you generate just functions/properties declaration (without body), and fill their bodies at the IR stage using IrGenerationExtension

But if you really want to generate this call at frontend, you can just write TODO() call in the source code, inspect it's content in the debugger (e.g. by implementing some empty function call checker, which will be called on this call) and accordingly initialize all required fields in buildFunctionCall

As for buildSimpleFunction, I don't recommend use it
There is a bunch of different utilities for creation of declaration from plugins (named create...), and it's better to use them
Check this file as an entrypoint
And here is an usage example